Ok, I am stumped, but maybe it’s me, since I am trying my first Android build. 
Using 2019.3.0b12, I followed these directions to install SDK, NDK, OpenJDK.
Updated Project Settings, added Publishing Settings info, and attempt to build, and this pops up.
Am I missing something? Any help appreciated?
Maybe try rebooting your machine? (Could just be a cached/stale environment variable issue.)
Thanks for the suggestion, but the system has been rebooted a few times. This error seems to remain over several days.
Check the editor log to see if there is any more useful information when this error occurs: 
Also, does the issue repro with an almost-empty Unity project? If so, file a bug through the Unity Editor and attach that repro project … that’s all I have left to suggest, I’m sorry. =(
There’s a known issue with installing the SDK, NDK and JDK via the Hub on Linux.
The workaround would be to use an external SDK & NDK, for instance downloaded through Android Studio.
The problem went away when I installed (and started using) 2019.3.0f1, so perhaps it this is just isolated to this version.
Thanks everyone!